"As above so below" this phrase is very common in the western mystery traditions.  The whole modern form is "As above so below; as below so above; as within so without; as without so within."

The phrase is attributed to Hermes Trismegistus ,"thrice-great Hermes", who is a syncretism of the Greek god Hermes and the Egyptian god Thoth. It was written on an emerald tablet reportedly found in his tomb.  The Emerald Tablet contained knowledge for how the fundamental laws of the universe work.  The true history of the tablet and of it's author is a very difficult one to navigate and is not the main point I have in this article.  Some legends of Hermes Trismegistus say he was a contemporary of the biblical Moses, or that he was an Egyptian Priest King who had learned the mysteries of the universe.  The Emerald Tablet has many translations and the writings of the tablet and the two books attributed to Hermes Trismegistus the Asclepius, and Corpus Hermeticum have a very debated history, but

"... they were certainly not written in remotest antiquity by an all wise Egyptian priest, as the Rennaissance believed, but by various unknown authors, all probably Greeks, and they contain popular Greek philosophy of the period, a mixture of Platonism and Stoicism, combined with some Jewish and probably some Persian influences." (Yates Giordano Bruno and the Hermetic Tradition pp. 2–3)

So in all probability the modern writings have many different historical influences. Here is a twelfth century Latin translation available at : http://www.sacred-texts.com/alc/emerald.htm

"0) When I entered into the cave, I received the tablet zaradi, which was inscribed, from between the hands of Hermes, in which I discovered these words:
1) True, without falsehood, certain, most certain.
2) What is above is like what is below, and what is below is like that which is above. To make the miracle of the one thing.
3) And as all things were made from contemplation of one, so all things were born from one adaptation.
4) Its father is the Sun, its mother is the Moon.
5) The wind carried it in its womb, the earth breast fed it.
6) It is the father of all ‘works of wonder' (Telesmi) in the world.
6a) Its power is complete (integra).
7) If cast to (turned towards- versa fuerit) earth,
7a) it will separate earth from fire, the subtile from the gross.
8) With great capacity it ascends from earth to heaven. Again it descends to earth, and takes back the power of the above and the below.
9) Thus you will receive the glory of the distinctiveness of the world. All obscurity will flee from you.
10) This is the whole most strong strength of all strength, for it overcomes all subtle things, and penetrates all solid things.
11a) Thus was the world created.
12) From this comes marvelous adaptions of which this is the proceedure.
13) Therefore I am called Hermes, because I have three parts of the wisdom of the whole world.
14) And complete is what I had to say about the work of the Sun, from the book of Galieni Alfachimi.
[From Latin in Steele and Singer 1928: 492.]"

The phrase also appears in the Kybalion in chapter two as one of the seven Hermetic principles.  “As above, so below; as below, so above.” is the Hermatic principle of Correspondence.  In this context it is used to show the correspondence between something you see and know to something you can not see or know.  In Hermeticism it is used to gain knowledge of the aspects of the spiritual realm we do not have access to here on Earth.  It is used as a philosophical tool to aid the student in penetrating the veal to grasp that which cannot be seen by man.

It also has function in Magick.  The "Above" represents the spiritual worlds and the "Below" our current home on Earth.  We are a reflection of the spiritual or astral worlds and they are a reflection of us.  Change one and you affect the other.  All ritual Magick and Folk Magick operates on the principle of sending your intent to make a change by manipulating either objects in folk Magick or symbols in ritual Magick that correspond with your desired change.  The change from a is made in the Astral worlds, so that the affect can be seen as the reflection of the Astral changes occur in the material world. The same things apply to our conscious and subconscious minds.  As "within"(subconscious) as "without" (conscious).  The subconscious mind is our doorway and communication link to the spiritual realms, so changes called for in the "above" that are to affect you will then be affected on your subconscious to affect you conscious.

I think we often forget though that this works both ways.  Change the material or the "below" and you change the Astral or the "above".  I always tell people what I was taught that before you do anything Magically you need to do everything possible in the mundane world first.  Changes in the mundane world affect the spiritual, and I have found in my personal practice if something can be accomplished easily in the mundane then Magickal attempts will often fall flat until you do the mundane tasks first.

The best approach is to pursue both options simultaneously.  We often forget or don't know the power of our own minds.  To make a change in the "above" the Astral or Spiritual worlds that you want to manifest in your "below" or material life all you really need to do is imagine it.  Just the simple act of thinking of an idea, seeing it in you head as if it was real; seeing that it has happened and feeling the emotions associated with the accomplishment of it is enough to make a change in the "above".  Have that same thought again the next day and you will strengthen the changes you made in the "above", until your material world will change to match the reflection of the Spiritual you have created with your detailed vision of it.

At home I always fell into the same pattern each night.  I had things I wanted to do, but I always seemed to get stuck.  I did several different approaches some psychological with positive affirmations to be productive or have energy.  I did several spells for the same things and I cleansed the area.  Each attempt would have an affect but it would not last.  I would fall back into he same patterns over and over.  I then realized that I had never changed the physical aspects of my home that where causing the behaviors i wanted to change.  I was trying to change the result of my own daily actions but not changes the environment.  I was concentrating on the way I wanted to feel and act, but not what was making me feel that way.  Repeatedly I would try to get more done, but after initial success find myself vegging on the couch again. My break through came when I realized I was successfully changing my "within" or the "above" and getting a desired manifestation, but my "below" the physical house, how it was set up the fact I was trying to do things exactly the same way as I had always done was then making the "above" back into the reflection of itself.  I had concentrated on just changing my personal energy level and my actions without considering the real cause of why I was not happy with how my house was organized.  It was not just that I needed to do more I needed to change the way I do things.  I changed the way I was doing my personal affirmations and my spell work to be towards changing the system in the house, and I rolled up my sleeves and began to see some real success.

Never forget that you have the power to change the world around you by remembering that "As above so below; as below so above".